This invention relates in general to communication systems and more particularly to a shared data/voice communication system wherein the data capacity may be programmed and maintained as desired and also wherein interference between voice and data traffic is effectively minimized.
Communication systems which process data information are becoming more and more common in the industry. In point of fact, systems which handle data only are relatively wide spread. Typically such radio data systems comprise a base station with full duplex capability, a network control processor (NCP), front end to a system host computer, and a plurality of portable radio data terminals operating in half duplex mode.
As may be expected, suitable channel access protocol arrangements are required to minimize terminal interference and keep the system operating with optimum efficiency. To this end, a protocol has been developed which has enjoyed wide spread application, referred to in the literature as "non-persistent busy tone (bit) multiple access". Basically, the protocol permits channel contention between radio data terminals. When one such terminal gains channel access and begins to transmit data, the base station informs/advises the other system data terminals of such by way of setting "inhibit bits" at predetermined locations or positions in the outbound data stream. When a data terminal encounters these inhibit bits, it waits for a random time before contending again for access to the channel. In this way, the system operates with minimum interference and an orderly process is established for all participating data terminals in the system to utilize the available capacity.
It should be noted that in such radio data systems, the information being communicated is in fact data. Without more, voice, or analog information, as such is not compatible. There are occasions, however, and increasingly so, where voice communications is very much desired. In some cases, it is absolutely essential. Of course, the user can communicate by voice with a separate mobile or portable unit operating on a completely different channel and/or communication system. As will be readily recognized, such option is quite expensive and, at the same time, inefficient.
There are, of course, systems that accommodate both voice and data on the same system, and even the same channel. However, these are primarily voice systems adapted to also accommodate in limited terms the transmission of data. They are primarily designed to effect channel management with suitable voice protocol arrangements which are not efficient for data management. Moreover, such systems have no means of guaranteeing the system will be used for a minimum level data transmission. Voice communication can and does frequently dominate system usage entirely.
What is needed is the ability to add to an existing efficiently operated data communication system the capability of voice communication as well, without changing the data access protocol being used therein. The addition of the voice communication capability should in no way increase the level of interference on such channel when units are operated in either voice or data mode. Moreover, there needs to be an effective means and method of guaranteeing that specific but programmable levels of data capacity are being utilized by the system even though it is shared by both the voice and data traffic.